/Engine/Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Public/PartyBeaconState.h
the stringified version of the enum passed in
namespace EPartyReservationResult { const TCHAR * EPartyReservationResult::ToString ( [EPartyReservationResult::Type](API\Plugins\OnlineSubsystemUtils\EPartyReservationResult__Type) SessionType ) }